The present invention relates generally to semiconductor packages and, more particularly, to a semiconductor package leadframe which includes support feet sized and configured to provide structural support to the die pad of the leadframe.
Integrated circuit dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the die and an underlying substrate such as a printed circuit board (PCB) or motherboard. The elements of such a package include a metal leadframe, a semiconductor die, bonding material to attach the die to the leadframe, bond wires which electrically connect pads or terminals on the die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior of the semiconductor package often referred to as the package body.
The leadframe is the central supporting structure of the semiconductor package. A portion of the leadframe is internal to the semiconductor package, i.e., completely surrounded by the plastic encapsulant forming the package body. Portions of the leads of the leadframe extend externally from the package body or are partially exposed therein for use in electrically connecting the semiconductor package to another component. In certain semiconductor packages, the die pad is downset or vertically recessed relative to portions of the leads which protrude from the package body of the semiconductor package.
To fabricate semiconductor packages, a current industry practice is to etch or stamp a thin sheet of metal to form a leadframe. The semiconductor die is mounted and wire bonded to the leadframe, with the encapsulant material forming the package body then being applied to encapsulate the die, bond wires, and portions of the leadframe in the above-described manner. Upon the hardening of the encapsulant material and resultant formation of the package body, portions of the leadframe are cut or singulated for purposes of electrically isolating the individual leads of the semiconductor package from each other.
In the fabrication of certain semiconductor packages, a molding procedure is conducted wherein the leadframe having the die wire bonded thereto is placed into the mold cavity of a mold, the mold cavity having the configuration of the fully formed package body of the semiconductor package. A molding compound is injected into the mold cavity of the mold, with the curing or solidification of the molding compound facilitating the formation of the package body of the semiconductor package, as indicated above. In the aforementioned molding process, a hydraulic press including upper and lower mold sections which collectively define the mold cavity is often used. Subsequent to the placement of the leadframe having the die wire bonded thereto into the mold cavity, pre-heated molding compound (e.g., epoxy resin) is injected into the gate of the mold, with the molding compound thereafter being transferred into the mold cavity for application to the leadframe and die wire bonded thereto.
As indicated above, in certain semiconductor packages such as Thin Quad Flat Package (TQFP) products, the die pad of the leadframe is downset relative to outer portions of the leads which protrude from the package body. The downset of the die pad causes the same to extend along a plane which is disposed in spaced, generally parallel relation to the plane along which the outer portions of the leads extend. Certain semiconductor packages such as Quad Flat Pack (QFP) products include a leadframe with a downset die pad and, when completed, have an overall thickness in the range of from about two to four mm. Due to this thickness, there is typically enough space defined between the die pad of the leadframe and the upper and lower sections of the mold such that the molding process is not affected by the spatial separation between the die pad and those surfaces of the upper and lower mold sections which collectively define the mold cavity.
There is an increasing demand in the electronics industry for QFP products including TQFP products of substantially reduced thickness (e.g., one mm or forty mils). The desired thickness reductions in semiconductor packages such as QFP and TQFP products which include a downset die pad often adversely affects the molding process used to form the package body of the semiconductor package. As indicated above, a typical TQFP product has a total thickness of approximately one mm or forty mils. Thus, when the leadframe having the die wire bonded thereto is placed into the mold cavity to facilitate the formation of the package body, the distance separating the die from the surface of the upper mold section partially defining the cavity is about 0.25 mm (about 10 mils), with the distance separating the die pad from the surface of the lower mold section partially defining the mold cavity being only about 0.2 mm (8 mils). The molding compound being filled into the mold cavity via the gate of the mold will flow above the semiconductor die and below the die pad. However, due to the downset of the die pad and the very small gap defined between the die pad and the lower mold section, the molding compound cannot easily flow beneath the die pad. On the other hand, the molding compound can easily flow rapidly above the die pad and the die mounted thereto because of the substantially greater space or distance separating the die from the upper mold section. As a result, the molding process becomes “unbalanced” due to the disparities in the pressure conditions existing above and below the die pad of the leadframe. As a result of this unbalanced state, the support bar of the leadframe which supports the die pad is pressed down by the pressure and weight of the molding compound flowing above the die pad. This downward pressure and weight often results in the die pad and possibly a portion of the lower surface of the die being exposed within the completed package body of the semiconductor package, thus making the semiconductor package unusable. The downward pressure applied to the die pad, though not necessarily resulting in the exposure of the die pad within the package body, sometimes results in poor adhesion between the package body and the die pad, and resultant delamination or separation of the package body from the die pad.
The present invention addresses and alleviates the above-described problems in making thin semiconductor packages including the leadframes with downset die pads by providing support feet on the die pad of the leadframe which prevent excessive movement of the die pad within the mold cavity during the molding operation used to form the package body of the semiconductor package. These and other features of the present invention will be described in more detail below.